The present invention relates in general to refrigeration systems, and more particularly to defrost gas conditioning means for air cooled reverse cycle defrost refrigeration systems.
On an air cooled reverse cycle defrost refrigeration system such as the "Ice-Master" Ice Maker produced by Morris and Associates of Raleigh, N.C., operating on a similar principal to the C. E. Lowe U.S. Pat. Nos. 3,280,585, or 3,026,686 or 3,034,310, when the machine goes on defrost the opening of the hot gas solenoid valve allows instantaneous release of the discharge gas pressure from the high side into the evaporator surface to accomplish the defrost as quickly and effectively as possible. It is estimated that approximately 1/2 of this hot gas required for defrost of the subject ice maker comes from the flash gas in the condenser at the time the defrost solenoid valve is opened. Tne balance of the heat required for the defrost comes more slowly and on a continuing basis from the discharge gas of the compressor as it continues to operate during the defrost cycle.
The suddeness of the pressure release when the solenoid valve opens causes an instantaneous "flashing" or boiling of any liquid refrigerant that may be in the condenser at the time together with a rapid versal of flow in both the condenser and discharge line to the condenser.
Depending on the amount of liquid in the air cooled condenser and tne pressures in the condenser before and after the pressure release as well as both the temperature and mass of the condenser itself, there is a very real possibility as a result that slugs of liquid refrigerant from the condenser will be carried back througn the discharge line and to the defrost solenoid and into the evaportors with tne possibility of damage to the lines from "hydraulic-hammer" as well as damage to the compressor from liquid slugging.
One possibility of solving this problem is to install a check valve in the compressor discharge line at the inlet to the condenser, but this would eliminate the benefits of the flash gas contribution to defrost which can amount to as much as 10% of the ice capacity of the system and may increase electric KWH per ton of ice as much as 10%.
Therefore, what is needed is a means of conditioning this warm defrost gas rushing back from the condenser so as to insure that no slugs of liquid refrigerant or oil that may be carried along with it can pass back into the discharge line from the condenser to cause the above problems.
This may be accomplished by a surge accumulator tank installed at the point where the compressor discharge line enters the air cooled condenser.
One other very significant characteristic of this type problem is that it occurs intermittently or spasmodically and is extremely hard to identify or predict because of the wide range of atmospheric conditions encountered in an air cooled system, especially one utilizing reverse cycle defrost. The tragedy is that it only takes one slug of liquid to either destroy a compressor or rupture a line and it occurs so fast that you may not be ab-e to figure out what happened.
Installation of a surge accumulator type defrost gas conditioner in accordance with the present invention proves to be the best remedy for this problem without incurring a severe penalty of capacity loss and increase of operating cost.